Lithium cell based on lithiated transition metal titanates

ABSTRACT

An electrochemical active material contains a lithiated zirconium, titanium, or mixed titanium/zirconium oxide. The oxide can be represented by the formula LiM′M″XO 4 , where M′ is a transition metal, M″ is an optional three valent non-transition metal, and X is zirconium, titanium, or a combination of the two. Preferably, M′ is nickel, cobalt, iron, manganese, vanadium, copper, chromium, molybdenum, niobium, or combinations thereof. The active material provides a useful composite electrode when combined with a polymeric binder and electrically conductive material. The active material can be made into a cathode for use in a secondary electrochemical cell. Rechargeable batteries may be made by connecting a number of such electrochemical cells.

FIELD OF THE INVENTION

[0001] The present invention relates to lithium cells based on lithiatedtransition metal titanates. More particularly, it provides activematerials useful as a cathode (positive electrode) active material andan anode (negative electrode) active material for use in secondaryelectrochemical cells.

BACKGROUND OF THE INVENTION

[0002] Lithium batteries are prepared from one or more electrochemicalcells. Non-aqueous lithium electrochemical cells typically include anegative electrode, a lithium electrolyte prepared from a lithium saltdissolved in one or more organic solvents, and a positive electrode ofan electrochemically active material, typically a chalcogenide of atransition metal. During discharge, lithium ions from the negativeelectrode pass through the liquid electrolyte to the electrochemicallyactive material of the positive electrode, where the ions are taken upwith the simultaneous release of electrical energy. Thus on discharge,the positive electrode functions as a cathode, and the negativeelectrode as an anode. To reflect this fact, the terms “positiveelectrode” and “cathode” will be used interchangeably in the descriptionand claims, as will the terms “negative electrode” and “anode”. Duringcharging, the flow of ions is reversed so that lithium ions pass fromthe positive electrode through the electrolyte and are plated back ontothe negative electrode.

[0003] Recently, the lithium metal anode has been replaced with a carbonanode such as coke or graphite in which lithium ions can be inserted toform Li_(x)C₆. In the operation of the cell, lithium passes from thecarbon through the electrolyte to the cathode where it is taken up justas in a cell with a metallic lithium anode. During recharge, the lithiumis transferred back to the anode where it re-inserts into the carbon.Because no metallic lithium is present in the cell, melting of the anodedoes not occur even under abusive conditions. Also, because lithium isreincorporated into the anode by insertion or intercalation rather thanby plating, dendritic and spongy lithium growth does not occur.Non-aqueous lithium electrochemical cells are discussed, for example, inU.S. Pat. Nos. 4,472,487, 4,668,595, and 5,028,500. These cells areoften referred to as “rocking chair” batteries because lithium ions moveback and forth between the insertion or intercalation compounds duringcharge/discharge cycles.

[0004] Known positive electrode active materials include LiCoO₂,LiMn₂O₄, and LiNiO₂. The cobalt compounds are relatively expensive andthe nickel compounds are difficult to synthesize. A relativelyeconomical positive electrode is LiMn₂O₄, for which methods of synthesisare known. The lithium cobalt oxide, the lithium manganese oxide, andthe lithium nickel oxide have a common disadvantage in that the chargecapacity of a cell comprising such cathodes may suffer a significantloss in capacity. That is, the initial capacity available (amphours/gram) from LiMn₂O₄, LiNiO₂, and LiCoO₂ is less than thetheoretical capacity because significantly less than 1 atomic unit oflithium engages in the electrochemical reaction. Such an initialcapacity value is significantly diminished during the first cycleoperation and such capacity further diminish in successive cycles ofoperation. For LiNiO₂ and LiCoO₂ only about 0.5 atomic units of lithiumis reversibly cycled during cell operation. Many attempts have been madeto reduce capacity fading, for example, as described in U.S. Pat. No.4,828,834 by Nagaura et al. However, the presently known and commonlyused, alkali transition metal oxide compounds suffer from relatively lowcapacity. Therefore, there remains the difficulty of obtaining alithium-containing electrode material having acceptable capacity withoutdisadvantage of significant capacity loss when used in a cell.

[0005] Japanese Patent No. 08180875 to Aichi Seiko discloses a lithiumsecondary battery having a cathode made of an active material consistingof a lithium metal titanate of structure LiTiMO₄ wherein M is manganese,iron, chromium, nickel, cobalt, magnesium, and/or boron.

[0006] Lithium ion technology, and the associated lithium containingcompounds useful as cathode active materials in such batteries, havegiven the industry needed flexibility in designing electrochemical cellsfor a wide variety of technological uses. However, the industry isconstantly seeking for new materials to provide even greater flexibilityin design parameters, ease of construction, and increased energydensity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is an x-ray diffraction pattern of LiVTiO₄ made fromlithium carbonate.

[0008]FIG. 2 is an x-ray diffraction pattern of LiVTiO₄ made fromlithium hydroxide.

[0009]FIG. 3 is an x-ray diffraction pattern of synthesized LiCrTiO₄.

[0010]FIG. 4 is an x-ray diffraction pattern of synthesized LiMnTiO₄.

[0011]FIG. 5 is an x-ray diffraction pattern of synthesized LiFeTiO₄.

[0012]FIG. 6 is an x-ray diffraction pattern of synthesized LiCoTiO₄.

[0013]FIG. 7 is a first cycle constant current data of LiVTiO₄ made fromlithium carbonate.

[0014]FIG. 8 shows electrode voltage data for LiVTiO₄ made from lithiumcarbonate.

[0015]FIG. 9 shows a differential capacity data for LiVTiO₄ made fromlithium carbonate.

[0016]FIG. 10 shows a first cycle constant current data of LiVTiO₄ madefrom lithium hydroxide.

[0017]FIG. 11 shows electrode voltage data for LiCrTiO₄ as cathode.

[0018]FIG. 12 shows differential capacity data for LiCrTiO₄ as cathode.

[0019]FIG. 13 shows electrode voltage data for LiCrTiO₄ as anode.

[0020]FIG. 14 shows differential capacity data for LiCrTiO₄ as anode.

SUMMARY OF THE INVENTION

[0021] The present invention provides an electrochemical active materialcontaining a lithiated zirconium, titanium, or mixed titanium/zirconiumoxide. The oxide can be represented by the formula LiM′_(a)M″_(1−a)XO₄,where M′ is a transition metal or combination of transition metals, M″is a non-transition metal, a is greater than zero and less than or equalto 1, and X is zirconium, titanium, or combinations thereof. Preferably,M′ is titanium, nickel, cobalt, iron, manganese, vanadium, copper,chromium, molybdenum, niobium, or combinations thereof. The activematerial provides a useful composite electrode when combined with apolymeric binder and electrically conductive material. The activematerial can be made into a cathode for use in a secondaryelectrochemical cell. Rechargeable batteries may be made by connecting anumber of such electrochemical cells.

[0022] In another embodiment, some of the materials may also be used asanode materials.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The active material of the present invention contains a lithiatedtitanium or zirconium oxide of general formula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0024] wherein M′ represents a transition metal or a mixture oftransition metals, M″ represents a non-transition metal or a mixture ofnon-transition metals, a and b are independently greater than or equalto 0 and less than or equal to 1, and n ranges from about 0.01 to 2.When n is less than 1.0, M′ and M″ must take on an average oxidationstate greater than +3. When n is greater than 1.0, then M′ and M″ musttake on an average oxidation state less than +3. Preferably, n is atleast 0.2, and more preferably at least 0.5. In a preferred embodiment,n is about 1.0. Preferred transition metals include titanium, vanadium,manganese, iron, chromium, nickel, cobalt, molybdenum, niobium, andcombinations thereof. When b is 1 (i.e., when the active materials aretitanates), M′ comprises at least vanadium. When b is equal to zero(i.e., when the active materials comprise zirconates), and M′ istitanium, an active material of the invention may be represented byLiTiZrO₄. Representative non-transition metals include aluminum, boron,indium, gallium, antimony, bismuth, thallium, and combinations thereof.

[0025] The active material can be mixed with a polymeric binder and anelectrically conductive material to form an electrode material. Theelectrode material can then be made into an electrode using conventionaltechniques. In a preferred embodiment, the active materials of theinvention serve as cathode (positive electrode) active materials. Thecathode active material of the invention may be mixed or diluted withanother cathode active material, electronically conducting material,solid electrolyte, or compatible inert material. A cathode is readilyfabricated from individual or mixed cathode active materials.

[0026] In one aspect, the active materials of the invention are lithiumvanadium titanates of general formula

Li_(n)VTiO₄

[0027] wherein n is from 0.01 to about 2. In one embodiment, the activematerials are the source of lithium in a lithium ion battery. In such anapplication, n is preferably at least 0.2, and more preferably at least0.5. In a preferred embodiment, n is 1.0.

[0028] In another aspect of the invention, the active materials containlithiated metal zirconates or mixed titanates and zirconates of generalformula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0029] wherein a is from 0 to 1, inclusive, and b is less than one andgreater than or equal to zero, n is from 0.01 to 2, M′ represents atransition metal or mixture of transition metals, and M″ represents anon-transition metal or mixture of non-transition metals. Preferably, nis at least 0.2, and more preferably at least 0.5. In a preferredembodiment, n is about 1.0. The transition metal M′ is preferablyselected from the group consisting of titanium, vanadium, manganese,iron, chromium, nickel, cobalt, molybdenum, niobium, and combinationsthereof. In a preferred embodiment, M′ is at least vanadium.

[0030] In yet another aspect of the invention, there are provided anodeor negative electrode active materials which are lithiated metaltitanates and/or zirconates represented by the general formula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄,

[0031] wherein n is from 0.01 to about 2, a is greater than zero andless than or equal to one, b is greater than or equal to zero and lessthan or equal to one, M′ is a transition metal or mixture of transitionmetals, and M″ represents a +3 non-transition metal or mixture ofnon-transition metals. Preferably, M′ comprises one or more transitionmetals selected from the group consisting of titanium, vanadium,manganese, iron, chromium, nickel, cobalt, molybdenum, and niobium. In apreferred embodiment, M′ is at least chromium. Preferably, n is at least0.2, and more preferably at least 0.5. In a preferred embodiment, n isabout 1.0.

[0032] Active materials having the formulas noted above are convenientlysynthesized by carrying out solid state reaction of starting materialswhich provide the metal elements and lithium of the active materials.For example, titanium and zirconium are conveniently provided astitanium dioxide and zirconium dioxide starting materials respectively.When the metals M, M′, and/or M″ are provided as oxide startingmaterials, the starting materials can be represented by the formulasM₂O₃, MO₂, and M₂O₅ for metals in an oxidation state of +3, +4, and +5respectively. It is also possible to provide the metals as hydroxides ofgeneral formula M(OH)₃, M(OH)₄ and the like for metals of differentoxidation states. A wide variety of materials is suitable as startingmaterial sources of lithium. One preferred lithium starting material islithium carbonate.

[0033] The solid state synthesis may be carried out with or withoutreduction. When the active materials are to be synthesized withoutreduction, the starting materials are simply combined in astoichiometric ratio and heated together to form active materials of thedesired stoichiometry. Active materials having a range of values n forthe lithium subscript can be made by providing metals M or mixtures ofmetals M′ and M″ in average oxidation states ranging from +2 (in whichcase n will be 2.0 for charge balance), to +3 (in which case n will be1.0 for charge balance) up to about 3.9 (in which case n will be 0.1) oreven up to 3.99 (for n=0.01). For example, the titanium or zirconium maybe provided in the +4 oxidation state, while the metals M andalternatively M′ or M″ are provided in a +3 oxidation state, for exampleas oxides or hydroxides, to form active materials where n is 1.0. Whenthe solid state reaction is carried out in the presence of a reducingagent, it is possible to use metals as starting materials havinginitially higher oxidation states, and it is possible to incorporatelithium at non-integer levels between about 0.01 and 2 as before. Duringthe reaction, the oxidation state of the starting material metal isreduced. Either the reducing agent or the lithium compound can serve aslimiting reagent. However, when the reducing agent is limiting, theactive material will contain unreacted lithium compound as an impurity.When the lithium containing compound is limiting, the reducing agentwill remain in excess after the reaction. Commonly used reducing agentsinclude elemental carbon and hydrogen gas as illustrated below in theExamples. In the case of carbon as a reducing agent, the remainingexcess carbon does not harm the active material because carbon is itselfpart of the electrodes made from such active materials. When thereducing agent is hydrogen gas, any excess reducing agent is notincorporated into the starting material because the hydrogen volatilizesand can be removed. For these reasons, it is preferred to carry outreductive solid state reactions where the lithium compound is limitingin a stoichiometric sense. By selecting the amount of lithium compoundas limiting reagent, it is possible to prepare lithiated titanium orzirconium oxides of general formula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0034] where n ranges from about 0.01 up to about 2. Formally, thetitanium/zirconium element is in a +4 oxidation state, while theoxidation state of M′ and M″ will take on an average oxidation state of+(4−n) to provide charge balance in the formula.

[0035] A preferred method of synthesis is a carbothermal reduction wherecarbon is used as reducing agent as discussed above. The reducing carbonmay be provided as elemental carbon, such as in the form of graphite orcarbon black. Alternatively, the reducing carbon may be generated insitu during the reaction by providing the reducing carbon in the form ofa precursor that decomposes or carbonizes to produce carbon during thereaction. Such precursors include, without limitation, cokes, starch,mineral oils, and glycerol and other organic materials, as well asorganic polymers that can form carbon material in situ on heating. In apreferred embodiment, the source of reducing carbon undergoescarbonization or decomposition at a temperature below which the otherstarting materials react.

[0036] Thus, the lithiated mixed metal titanates/zirconates of theinvention can be prepared with a carbothermal preparation method usingas starting materials a lithium source, a titanium and/or zirconiumcompound or compounds, and a metal source. Examples of lithium sourcesinclude without limitation lithium acetate, lithium hydroxide, lithiumnitrate, lithium oxalate, lithium oxide, lithium phosphate, lithiumdihydrogen phosphate and lithium carbonate, as well as hydrates of theabove. Mixtures of the lithium sources can also be used. Examples ofmetal sources include, without limitation, carbonates, phosphates,sulfates, oxides, hydroxides, carboxylates, acetates, silicates, andother compounds of transition metals and non-transition metals.Non-transition metals include boron, the lanthanide series metals, andthe alkaline earth metals, as well as the elements Al, Ga, In, Tl, Ge,Sn, Pb, Sb, Bi, and Po. Mixtures of metal sources may be used. Preferredmetal sources include the oxides, dioxides, trioxides and hydroxidesdiscussed above. In a preferred embodiment, the metal source is chosenfrom among compounds of metals M′ and M″ as defined in the formulaabove. The titanium and/or zirconium compounds can be selected from awide range of compounds, including those described above for the metalsource, as well as titanates or zirconates such as lithium titanate andlithium zirconate. Preferred zirconium and titanium compounds includetitanium dioxide, zirconium dioxide, and combinations thereof.

[0037] In the carbothermal reductive method, the starting materials aremixed together with reducing carbon, which is included in an amountsufficient to reduce a metal ion of one or more of the metal-containingstarting materials. The carbothermal conditions are set such as toensure the metal ion does not undergo full reduction to the elementalstate. Excess quantities of one or more starting materials other thancarbon may be used to enhance product quality. For example, a 5% to 10%excess may be used. The carbon starting material may also be used inexcess. When the carbon is used in stoichiometric excess over thatrequired to react as reductant with the molybdenum source, an amount ofcarbon, remaining after the reaction, functions as a conductiveconstituent in the ultimate electrode formulation. This is consideredadvantageous for the further reason that such remaining carbon will ingeneral be intimately mixed with the product active material.Accordingly, excess carbon is preferred for use in the process, and maybe present in a stoichiometric excess amount of 100% or greater. Thecarbon present during compound formation is thought to be intimatelydispersed throughout the precursor and product. This provides manyadvantages, including the enhanced conductivity of the product. Thepresence of carbon particles in the starting materials is also thoughtto provide nucleation sites for the production of the product crystals.

[0038] The starting materials are intimately mixed and then reactedtogether where the reaction is initiated by heat and is preferablyconducted in a non-oxidizing, inert atmosphere. Before reacting thecompounds, the particles are mixed or intermingled to form anessentially homogeneous powder mixture of the precursors. In one aspect,the precursor powders are dry-mixed using a ball mill and mixing media,such as zirconia. Then the mixed powders are pressed into pellets. Inanother aspect, the precursor powders are mixed with a binder. Thebinder is selected so as to not inhibit reaction between particles ofthe powders. Therefore, preferred binders decompose or evaporate at atemperature less than the reaction temperature. Examples include,without limitation, mineral oils, glycerol, and polymers that decomposeto form a carbon residue before the reaction starts. In still anotheraspect, intermingling can be accomplished by forming a wet mixture usinga volatile solvent and then the intermingled particles are pressedtogether in pellet form to provide good grain-to-grain contact.

[0039] Although it is desired that the precursor compounds be present ina proportion which provides the stated general formula of the product,the lithium compound may be present in an excess amount on the order of5 percent excess lithium compared to a stoichiometric mixture of theprecursors. As noted earlier, carbon may be present in stoichiometricexcess of 100% or greater. A number of lithium compounds are availableas precursors, such as lithium acetate (LiOCOCH₃), lithium hydroxide,lithium nitrate (LiNO₃), lithium oxalate (Li₂C₂O₄), lithium oxide(Li₂O), lithium phosphate (Li₃PO₄), lithium dihydrogen phosphate(LiH₂PO₄), and lithium carbonate (Li₂CO₃). Preferred lithium sourcesinclude those having a melting point higher than the temperature ofreaction. In such cases, the lithium source tends to decompose in thepresence of the other precursors and/or to effectively react with theother precursors before melting. For example, lithium carbonate has amelting point over 600° C. and commonly reacts with the other precursorsbefore melting.

[0040] The method of the invention is able to be conducted as aneconomical carbothermal-based process with a wide variety of precursorsand over a relatively broad temperature range. The reaction temperaturefor reduction depends on the metal-oxide thermodynamics, for example, asdescribed in Ellingham diagrams showing the ΔG (Gibbs Free EnergyChange) versus T (temperature) relationship. As described earlier, it isdesirable to conduct the reaction at a temperature where the lithiumcompound reacts before melting. In general, the temperature shoulddesirably be about 400° C. or greater, preferably 450° C. or greater,and more preferably 500° C. or greater. Higher temperatures arepreferred because the reaction generally will normally proceed at afaster rate at higher temperatures. The various reactions involveproduction of CO or CO₂ as an effluent gas. The equilibrium at highertemperature favors CO formation.

[0041] Generally, higher temperature reactions produce CO effluent whilelower temperatures result in CO₂ formation from the starting materialcarbon. At higher temperatures where CO formation is preferred, thestoichiometry requires more carbon be used than the case where CO₂ isproduced. The C to CO₂ reaction involves an increase in carbon oxidationstate of +4 (from 0 to 4) and the C to CO reaction involves an increasein carbon oxidation state of +2 (from ground state zero to 2). Here,higher temperature generally refers to a range above about 650° C. Whilethere is not believed to be a theoretical upper limit, it is thoughtthat temperatures higher than 1200° C. are not needed. Also, for a givenreaction with a given amount of carbon reductant, the higher thetemperature the stronger the reducing conditions.

[0042] In one aspect, the method of the invention utilizes the reducingcapabilities of carbon in a controlled manner to produce desiredproducts having structure and lithium content suitable for electrodeactive materials. The method of the invention makes it possible toproduce products containing lithium, metal and oxygen in an economicaland convenient process. The ability to lithiate precursors, and changethe oxidation state of a metal without causing abstraction of oxygenfrom a precursor is advantageous. The advantages are at least in partachieved by the reductant, carbon, having an oxide whose free energy offormation becomes more negative as temperature increases. Such oxide ofcarbon is more stable at high temperature than at low temperature. Thisfeature is used to produce products having one or more metal ions in areduced oxidation state relative to the precursor metal ion oxidationstate. The method utilizes an effective combination of quantity ofcarbon, time and temperature to produce new products and to produceknown products in a new way.

[0043] Referring back to the discussion of temperature, at about 700° C.both the carbon to carbon monoxide and the carbon to carbon dioxidereactions are occurring. At closer to 600° C. the C to CO₂ reaction isthe dominant reaction. At closer to 800° C. the C to CO reaction isdominant. Since the reducing effect of the C to CO₂ reaction is greater,the result is that less carbon is needed per atomic unit of metal to bereduced. In the case of carbon to carbon monoxide, each atomic unit ofcarbon is oxidized from ground state zero to plus 2. Thus, for eachatomic unit of metal ion (M) which is being reduced by one oxidationstate, one half atomic unit of carbon is required. In the case of thecarbon to carbon dioxide reaction, one quarter atomic unit of carbon isstoichiometrically required for each atomic unit of metal ion (M) whichis reduced by one oxidation state, because carbon goes from ground statezero to a plus 4 oxidation state. These same relationships apply foreach such metal ion being reduced and for each unit reduction inoxidation state desired.

[0044] It is preferred to heat the starting materials at a ramp rate ofa fraction of a degree to 10° C. per minute and preferably about 2° C.per minute. Once the desired reaction temperature is attained, thereactants (starting materials) may be held at the reaction temperaturefor several hours. Although the reaction may be carried out in oxygen orair, the heating is preferably conducted under an essentiallynon-oxidizing atmosphere. The atmosphere is preferably essentiallynon-oxidizing so as not to interfere with the reduction reactions takingplace. An essentially non-oxidizing atmosphere can be achieved, forexample, through the use of vacuum or inert gases such as argon.Although some oxidizing gas (such as oxygen or air) may be present, itshould not be at so great a concentration that it interferes with thecarbothermal reduction or lowers the quality of the reaction product. Itis believed that any oxidizing gas present will tend to react with thecarbon and lower the availability of the carbon for participation in thereaction. To a large extent, such a contingency can be anticipated andaccommodated by providing an appropriate excess of carbon as a startingmaterial. Nevertheless, it is generally preferred to carry out thecarbothermal reduction in an atmosphere containing as little oxidizinggas as practical.

[0045] Advantageously, a reducing atmosphere is not required, althoughit may be used if desired. After reaction, the products are preferablycooled from the elevated temperature to ambient (room) temperature(i.e., 10° C. to 40° C.). Desirably, the cooling occurs at a ratesimilar to the earlier ramp rate, and preferably 2° C./minute cooling.Such cooling rate has been found to be adequate to achieve the desiredstructure of the final product. It is also possible to quench theproducts at a cooling rate on the order of about 100° C./minute. In someinstances, such rapid cooling (quench) may be preferred.

[0046] The invention also provides for electrochemical cells made fromelectrodes containing the active materials described above. Anelectrochemical cell contains an anode and a cathode. In one embodiment,the electrochemical cells include a cathode containing the activematerial of the present invention and an intercalation based anode, withboth anode and cathode capable of reversibly incorporating, byintercalation or other insertion process, an alkali metal ion. Theelectrochemical cells also contain an electrolyte composition which in apreferred embodiment contains a polymeric matrix and an electrolytesolution. The electrolyte solution is made up of an organic electrolytesolvent and a salt of an alkali metal. Each electrode preferably has acurrent collector.

[0047] Rechargeable batteries of the invention may be made byinterconnecting two or more electrochemical cells of the invention in anappropriate series/parallel arrangement to provide the requiredoperating voltage in current levels.

[0048] Lithium ion batteries containing cathodes having active materialsof the invention are generally operated according to known principles.An electrochemical cell is first provided in a discharged state. In thedischarged state, the cathode or positive electrode contains an activematerial based on a compound of general structure

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0049] wherein n is from about 0.01 to 2, a is greater than zero andless than or equal to 1, and b is from 0 to 1. M′ comprises one ortransition metals, preferably selected from the group consisting oftitainium, vanadium, manganese, iron, chromium, nickel, cobalt,molybdenum, and niobium, with the proviso that when b is 1, M′ comprisesat least vanadium. M″ is selected from the group consisting of aluminum,boron, indium, gallium, antimony, bismuth, thallium, and combinationsthereof.

[0050] The subscript n gives the number of lithium ions in the activematerial of the invention. It can range from fractional values that arequite low, up to values greater than 1 and as high as two. It can takeon values between the two extremes according to the desired properties,such as theoretical specific capacity of the active material or thedischarge capacity of the battery. It is preferably greater than about0.5 and will commonly be close to or equal to 1.0.

[0051] After the electrochemical cell is provided as above in thedischarged condition, it is put through a charging step to produce abattery in a charged or partially charged condition. Charging isgenerally accomplished by applying an outside electromotive force to thecell so as to cause the migration of lithium ions from the cathode tothe anode. The anode contains an insertion or intercalation materialsuch as carbon. Migration of lithium ions to the anode results ininsertion of lithium into the lattice of the insertion material. At thesame time, lithium is removed from the cathode, until an amount c isremoved. When charged, the anode thus contains insertion material withinserted lithium atoms. For example, when the insertion material of theanode is graphitic, the inserted lithium atoms form a composition thatcan be represented by the formula Li_(m)C₆, where m represents thefractional content of lithium in the carbon environment.Correspondingly, the cathode in the charged battery has a loweredlithium content. The cathode material can be represented as

Li_(n−c)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0052] where c represents an amount of lithium ions removed or removablefrom the cathode during the charging step. In this example, it can beseen that the cathode material in the uncharged and charged conditionscan be represented by the last formula above. In the (first) unchargedcondition, c is equal to 0. In the (second) charged or partially chargedcondition, c is greater than 0. It will be appreciated that in theformula above, c reaches a maximum value characteristic of the materialat the point at which the cell is fully charged. At intermediate stagesof the charging process, c takes on a value greater that zero but lessthan its maximum.

[0053] After charging, the cell is put through a discharging process.Typically, a load is applied to a circuit containing the battery orcell, and current flow from the battery or cell is used to operate theload. During discharge, lithium ions migrate to the cathode, along withelectrons (via the external circuit) that cause the reduction of thecathode material. Lithium ions are re-inserted into the cathode.Generally, a first cycle charge inefficiency is observed due, it isbelieved, to creation of a passivation film on the anode. On subsequentcycles with high-quality electrode or cathode materials, the amount oflithium extracted on charging will be approximately the same as theamount of lithium re-inserted on discharging. Cells containing suchhigh-quality materials are generally preferred because theirreversibility leads to a longer cycle life, so that the battery can becharged and re-charged a number of times.

[0054] When the active material of the invention is used as an anodematerial, the operation of the battery is similar. As before, thebattery is first prepared in a discharged condition, with the anodecontaining active material of formula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0055] where n, a, b, M′, and M″ are as defined above. The activematerial serves as a lithium insertion material analogously to thecarbonaceous insertion anode described above.

[0056] After construction, the battery is first put through a chargingprocess. During charging, lithium ions from the cathode migrate to theanode, where they are inserted in the active anode material to form amaterial that can be represented by the formula

Li_(n+c)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0057] where c represents the amount of lithium inserted into the anodeactive material during the charging step. It can be seen that the anodematerial in the uncharged and charged states can be represented by thelast formula above. In the first (uncharged) condition, c is equal to 0.In the (second) charged condition, c is greater than 0. As before, creaches a maximum characteristic of the material at the point at whichthe cell is fully charged. At intermediates stages of charging, c takeson a value greater than 0 but less than its maximum.

[0058] After charging, the cell is put through a discharging process, asbefore. During discharge, lithium ions are re-inserted into the cathodematerial. With high quality anode materials, the amount of lithiuminserted during the charging step and the amount of lithium extracted ondischarge will be approximately the same so that a highly reversiblecell is formed, leading to long cycle life and re-chargeability in abattery, as indicated above.

[0059] Reversibility of electrochemical cells made with active materialsof the invention can be explained on a chemical basis as shown above.That is, in reversible cells, theoretically the amount of lithium beingshuttled between the anode and cathode on successive charge/dischargecycles remains relatively constant. The extent of the change in theamount of lithium transferred between electrodes over time can beobserved in measurements of capacity fade.

[0060] In preferred embodiments, both the anode and cathode include acurrent collector that comprises, for example, a foil, a screen, grid,expanded metal, woven or non-woven fabric, or knitted wire formed froman electron conductive material such as metals or alloys. Particularlypreferred current collectors comprise perforated metal foils or sheets.In order to minimize the weight of the electrochemical cell, thincurrent collectors are preferred. Each current collector is alsoconnected to a current collector tab which extends from the edge of thecurrent collector. The anode tabs can be welded together and connectedto a lead. The cathode tabs are similar welded and connected to a lead.External loads can be electrically connected to the leads. Currentcollectors and tabs are described in U.S. Pat. Nos. 4,925,752,5,011,501, and 5,326,653, which are incorporated herein by reference.

[0061] In addition to the anode and cathode, the cells and batteries ofthe invention contain an electrolyte composition. The electrolytecomposition generally contains from about 5 to about 25% preferably fromabout 10 to about 20%, and more preferably from about 10-15% of aninorganic salt wherein the percentages are based on the total weight ofthe electrolyte composition. The percentage of salt depends on the typeof salt and electrolytic solvent employed.

[0062] The inorganic ion salt of the electrolyte composition refers toany salt suitable in a non-aqueous electrolyte composition.Representative examples of suitable inorganic ion salts are metal saltsof less mobile anions of weak bases having a large anionic radius.Examples of such anions include without limitation, I⁻, Br⁻, SCN⁻, ClO₄⁻, BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, CF₃COO⁻, CF₃SO₃ ⁻, N(SO₂CF₃)₂ ⁻, and the like.Specific examples of suitable inorganic ion salts include, withoutlimitation, LiClO₄, LiSCN, LiBF₄, LiAsF₆, LiCF₃SO₃, LiPF₆, (CF₃SO₂)₂NLi,(CF₃SO₂)₃CLi, NaSCN, and the like. The inorganic ion salt preferablycontains at least one cation selected from the group consisting of Li,Na, Cs, Rb, Ag, Cu, Mg and K.

[0063] The electrolyte composition further contains up to about 95weight percent of a solvent based on the total weight of the electrolytecomposition. The solvent of the electrolyte composition is generally alow molecular weight organic solvent added to the electrolytecomposition which may also serve the purpose of solvating the inorganicion salt. The solvent can in general be any compatible, relativelynon-volatile, and relatively polar aprotic solvent. Preferably, thesolvents have boiling points greater than about 85° C. to simplifymanufacture and increase the life of the electrolyte and battery.Typical examples of suitable solvents include organic carbonates as wellas other solvents such as gamma-butyrolactone, triglyme, tetraglyme,dimethylsulfoxide, dioxolane, sulfolane, and mixtures thereof. Whenusing propylene carbonate based electrolytes in an electrolytic cellwith graphite anodes, a sequestering agent, such as a crown ether, canbe added in the electrolyte.

[0064] Suitable organic carbonates are in general those with no morethan about twelve carbon atoms, and which do not contain any hydroxylgroups. Preferably, the organic carbonate is an aliphatic carbonate andmore preferably a cyclic aliphatic carbonate.

[0065] Suitable cyclic aliphatic carbonates for use in this inventioninclude 1,3-dioxolan-2-one (ethylene carbonate);4-methyl-1,3-dioxolan-2-one (propylene carbonate);4,5-dimethyl-1,3-dioxolan-2-one; 4-ethyl-1,3-dioxolan-2-one;4,4-dimethyl-1,3-dioxolan-2-one; 4-methyl-5-ethyl-1,3-dioxolan-2-one;4,5-diethyl-1,3-dioxolan-2-one; 4,4-diethyl-1,3-dioxolan-2-one;4,4-dimethyl-1,3-dioxan-2-one; 5,5-dimethy-1,3-dioxan-2-one;5-methyl-1,3-dioxan-2-one; 4-methyl-1,3-dioxan-2-one;5,5-diethyl-1,3-dioxan-2-one; 4,6-dimethyl-1,3-dioxan-2-one; and4,4,6-trimethyl-1,3-dioxan-2-one.

[0066] Linear aliphatic carbonates are also suitable for use in theinvention. Examples include, without limitation, dimethyl carbonate(DMC), dipropyl carbonate (DPC), diethyl carbonate (DEC), methyl ethylcarbonate (MEC), and the like.

[0067] Several of these cyclic and linear aliphatic carbonates arecommercially available such as propylene carbonate, ethylene carbonate,and dimethyl carbonate.

[0068] In one embodiment, the electrolyte composition also contains fromabout 5 to about 30 weight percent, preferably from about 15 to about 25weight percent of a solid polymeric matrix based on the total weight ofthe electrolyte composition. In this embodiment, suitable solidpolymeric matrixes are well known in the art and include inorganicpolymers, organic polymers, or a mixture of organic polymers withinorganic non-polymeric materials. Suitable inorganic non-polymericmaterials include without limitation, β-alumina, silver oxide, lithiumiodide, and the like.

[0069] The anode of the electrochemical cells of the invention typicallycomprises a compatible anodic material which is any material whichfunctions as an anode in a solid electrolytic cell, such as, in certaincases, the anode negative active materials of the present invention.Other compatible anodic materials are well known in the art include,without limitation, lithium, lithium alloys, such as alloys of lithiumwith aluminum, mercury, manganese, iron, zinc, and insertion orintercalation based anodes such as those employing carbon, tungstenoxides, and the like. Preferred anodes include lithium insertion- orintercalation anodes employing carbon materials such as graphite, cokes,mesocarbons, and the like. Such carbon insertion-based anodes typicallyinclude a polymeric binder having a molecular weight of from about1,000-5,000,000, and optionally, an extractable plasticizer suitable forforming a bound porous composite. Examples of suitable polymeric bindersinclude, without limitation, EPDM (ethylene propylene diaminetermonomer), PVDF (polyvinylidene difluoride), EAA (ethylene acrylicacid copolymer), EVA (ethylene vinyl acetate copolymer), EAA/EVAcopolymers, vinylidene fluoride hexafluoropropylene copolymers, and thelike.

[0070] The cathode typically comprises a compatible cathodic materialwhich is any material that functions as a positive pole in anelectrolytic cell. The cathode of the present invention includes thelithiated transition metal zirconium or titanium oxides of the presentinvention, but may also include other cathodic materials. Such othercathodic materials may include, by way of example, transition metaloxides, sulfides, and selenides, including lithiated compounds thereof.Representative materials include cobalt oxides, manganese oxides,molybdenum oxides, vanadium oxides, sulfides of titanium, molybdenum andniobium, the various chromium oxides, copper oxides, lithiated cobaltoxides, e.g., LiCoO₂ and LiCoVO₄, lithiated manganese oxides, e.g.,LiMn₂O₄, lithiated nickel oxides, e.g., LiNiO₂ and LiNiVO₄, and mixturesthereof. Cathode-active material blends of Li_(x)Mn₂O₄ (spinel) isdescribed in U.S. Pat. No. 5,429,890 which is incorporated herein. Theblends can include Li_(x)Mn₂O₄ (spinel) and at least one lithiated metaloxide selected from Li_(x)NiO₂ and Li_(x)CoO₂ wherein 0<x≦2. Blends canalso include Li_(y)-α-MnO₂ (0≦y<1) which is Li_(y)NH₄Mn₈O₁₆ (0≦y<1)which has a hollandite-type structure. Li_(y)-α-MnO₂ where 0≦y<0.5 ispreferred. α-MnO₂ can be synthesized by precipitation from a reactionbetween a MnSO₄ solution and (NH₄)₂S₂O₈ as an oxidizing agent.

[0071] In a preferred embodiment, the compatible cathodic material ofthe present invention is mixed with a polymeric binder such as describedabove in regard to the anode.

[0072] The cathode and anode generally further comprise one or moreelectrically conductive materials. Examples of such materials include,without limitation, graphite, powdered carbon, powdered nickel, metalparticles, and conductive polymers. Conductive polymers arecharacterized by a conjugate network of double bonds. Examples include,without limitation, polypyrrole and polyacetylene.

[0073] The invention has been described above with respect to particularpreferred embodiments. Further non-limiting examples of the inventionare given in the examples that follow.

EXAMPLES

[0074] General methods for preparation of the various active materialsof the invention will be described in this section. In some cases,materials prepared in the Examples are further characterized byelectrochemical and other means. The results of such characterizationare given in the Figures and the discussion below. A Siemens D500 X-rayDiffractometer equipped with Cu K_(α) radiation (λ=1.54056 Å) was usedfor X-ray diffraction (XRD) studies of the prepared materials.

[0075] The Examples give synthesis schemes for preparing compounds ofthe general formula

LiM′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0076] wherein M′ represents a transition metal, M″ represents a valence+3 non-transition metal, a and b are independently greater than or equalto 0 and less than or equal to 1. That is, in the embodimentsexemplified below, lithium is present in the compounds at a molar amountof unity. It is to be understood that active materials having non-unityvalues of lithium content can be prepared by using as starting materialsrelatively more or less lithium compound.

[0077] To illustrate, compounds of general structureLinM′aM″_(1−a)TibZr_(1−b)O₄ can be prepared according to the Examples byusing as starting material an amount of 0.5 n Li₂CO₃ instead of thelisted 0.5.

Example 1 Preparation of LiVTiO₄ from Li₂CO₃/TiO₂/V₂O₃

[0078] The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.5V₂O₃→LiVTiO₄+0.5CO₂

[0079] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

[0080] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0081] 0.5 g-mol of V₂O₃ is equivalent to 74.94 g

[0082] 1.740 g of Li₂CO₃ (Pacific Lithium Company), 3.760 g of TiO₂(Aldrich Chemical) and 3.530 g of V₂O₃ (Alfa Aesar) were used. Theprecursors were initially pre-mixed using a mortar and pestle and themixture was then pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Thesample was heated at a ramp rate of 2°/minute to an ultimate temperatureof 900° C. and maintained at this temperature for 8 hours. The samplewas then cooled to room temperature, before being removed from the tubefurnace for analysis. The powderized sample showed good uniformity, washard and appeared gray in color with a black metallic sheen.

[0083]FIG. 1 shows the x-ray diffraction pattern for this LiVTiO₄sample. The data appear fully consistent with the published data ofArillo et al., Solid State Ionics volume 107, page 307, published in1998, for the compositionally similar LiFeTiO₄. In the Fe material thex-ray diffraction data is consistent for a cubic spinel structure withthe space group Fd3m.

Example 2 Preparation of LiVTiO₄ from LiOH.H₂O/TiO₂/V₂O₃

[0084] The general reaction may be summarized:

LiOH.H₂O+TiO₂+0.5V₂O₃→LiVTiO₄+1.5H₂O

[0085] 1.0 g-mol of LiOH.H₂O is equivalent to 41.96 g

[0086] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0087] 0.5 g-mol of V₂O₃ is equivalent to 74.94 g

[0088] 1.24 g of LiOH.H₂O (Aldrich Chemical), 2.35 g of TiO₂ (AldrichChemical) and 2.21 g of V₂O₃ (Alfa Aesar) were used. The precursors wereinitially pre-mixed using a mortar and pestle and the mixture was thenpelletized. The pellet was then transferred to a temperature-controlledtube furnace equipped with an argon gas flow. The sample was heated at aramp rate of 2°/minute to an ultimate temperature of 900° C. andmaintained at this temperature for 8 hours. The sample was then cooledto room temperature, before being removed from the tube furnace foranalysis. The powderized sample showed reasonable uniformity, was hardand appeared black in color.

[0089]FIG. 2 shows the x-ray diffraction pattern for this LiVTiO₄sample. The data appear fully consistent with the published data ofArillo et al. Solid State Ionics 107, 307 (1998) for the compositionallysimilar LiFeTiO₄. In the Fe material the x-ray diffraction data isconsistent for a cubic spinel structure with the space group Fd3m.

Example 3 Preparation of LiVTiO₄ from Li₂CO₃/TiO₂/V₂O₅ (Under a ReducingAtmosphere)

[0090] The general reaction, conducted under a flowing hydrogenatmosphere, may be summarized:

H₂+0.5Li₂CO₃+TiO₂+0.5V₂O₅→LiVTiO₄+0.5CO₂+H₂O

[0091] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

[0092] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0093] 0.5 g-mol of V₂O₅ is equivalent to 90.94 g

[0094] 1.74 g of Li₂CO₃ (Pacific Lithium Company), 3.76 g of TiO₂(Aldrich Chemical) and 4.28 g of V₂O₅ (Alfa Aesar) were used. Theprecursors were initially pre-mixed using a mortar and pestle and themixture was then pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with a hydrogen gas flow.The sample was heated at a ramp rate of 2°/minute to an ultimatetemperature of 900° C. and maintained at this temperature for 8 hours.The sample was then cooled to room temperature, before being removedfrom the tube furnace for analysis. The powderized sample was soft andappeared black in color.

Example 4 Preparation of LiVTiO₄ from Li₂CO₃/TiO₂/V₂O₅ UsingCarbothermal Reduction

[0095] The general reaction, conducted under an inert atmosphere, may besummarized:

0.5Li₂CO₃+TiO₂+0.5V₂O₅+C→LiVTiO₄+0.5CO₂+CO

[0096] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

[0097] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0098] 0.5 g-mol of V₂O₅ is equivalent to 90.94 g

[0099] The precursors are initially pre-mixed, in the proportions shownabove, using a mortar and pestle and then pelletized. The pellet is thentransferred to a temperature-controlled tube furnace equipped with aninert atmosphere gas flow. The sample is then heated at an appropriaterate to an ultimate temperature in the approximate range 650-900° C. Thechosen temperature range assumes the a C→CO carbothermal reductionmechanism. The sample is maintained at this temperature for a time longenough to ensure complete reaction. The sample is then cooled to roomtemperature, before being removed from the tube furnace for analysis.

Example 5 Preparation of LiCrTiO₄ from Li₂CO₃/TiO₂/Cr₂O₃

[0100] The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.5Cr₂O₃→LiCrTiO₄+0.5CO₂

[0101] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

[0102] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0103] 0.5 g-mol of Cr₂O₃ is equivalent to 76.00 g

[0104] 1.73 g of Li₂CO₃ (Pacific Lithium Company), 3.56 g of TiO₂(Aldrich Chemical) and 3.74 g of Cr₂O₃ (Alfa Aesar) were used. Theprecursors were initially pre-mixed using a mortar and pestle and themixture was then pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Thesample was heated at a ramp rate of 2°/minute to an ultimate temperatureof 900° C. and maintained at this temperature for 8 hours. The samplewas then cooled to room temperature, before being removed from the tubefurnace for analysis. The powderized sample showed good uniformity, andappeared yellow/green in color.

[0105]FIG. 3 shows the x-ray diffraction pattern for this LiCrTiO₄sample. Structural refinement gave cubic space group Fd3m, a=8.397 Å,and a unit cell volume of 592.14 Å³. The data appear fully consistentwith the published data of Arillo et al. Solid State Ionics 107, 307(1998) for the compositionally similar LiFeTiO₄. In the Fe material thex-ray diffraction data is consistent for a cubic spinel structure withthe space group Fd3m.

Example 6 Preparation of LiMnTiO₄ from Li₂CO₃/TiO₂/Mn₂O₃

[0106] The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.5Mn₂O₃→LiMnTiO₄+0.5CO₂

[0107] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

[0108] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0109] 0.5 g-mol of Mn₂O₃ is equivalent to 78.94 g

[0110] 1.70 g of Li₂CO₃ (Pacific Lithium Company), 3.68 g of TiO₂(Aldrich Chemical) and 3.63 g of Mn₂O₃ (Alfa Aesar) were used. Theprecursors were initially pre-mixed using a mortar and pestle and themixture was then pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Thesample was heated at a ramp rate of 2°/minute to an ultimate temperatureof 900° C. and maintained at this temperature for 8 hours. The samplewas then cooled to room temperature, before being removed from the tubefurnace for analysis. The powderized sample showed good uniformity, wassemi-hard and appeared black/gray in color.

[0111]FIG. 4 shows the x-ray diffraction pattern for this LiMnTiO₄sample. The data appear fully consistent with the published data ofArillo et al. Solid State Ionics 107, 307 (1998) for the compositionallysimilar LiFeTiO₄. In the Fe material the x-ray diffraction data isconsistent for a cubic spinel structure with the space group Fd3m.

Example 7 Preparation of LiFeTiO₄ from Li₂CO₃/TiO₂/Fe₂O₃

[0112] The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.5Fe₂O₃→LiFeTiO₄+0.5CO₂

[0113] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

[0114] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0115] 0.5 g-mol of Fe₂O₃ is equivalent to 79.85 g

[0116] 1.69 g of Li₂CO₃ (Pacific Lithium Company), 3.66 g of TiO₂(Aldrich Chemical) and 3.66 g of Fe₂O₃ (Aldrich Chemical) were used. Theprecursors were initially pre-mixed using a mortar and pestle and themixture was then pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Thesample was heated at a ramp rate of 2°/minute to an ultimate temperatureof 900° C. and maintained at this temperature for 8 hours. The samplewas then cooled to room temperature, before being removed from the tubefurnace for analysis. The powderized sample showed good uniformity, wasvery hard and appeared brick red in color.

[0117]FIG. 5 shows the x-ray diffraction pattern for this LiFeTiO₄sample. Structural refinement gives cubic space group Fd3m, a=8.432 Åand a unit cell volume of 581.96 Å3. This is isostructural with thepublished data of Arillo et al. Solid State Ionics 107, 307 (1998) fortheir own prepared LiFeTiO₄ material.

Example 8 Preparation of LiCoTiO₄ from LiCoO₂/TiO₂

[0118] The general reaction may be summarized:

LiCoO₂+TiO₂→LiCoTiO₄

[0119] 1.0 g-mol of LiCoO₂ is equivalent to 97.87 g

[0120] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0121] 4.40 g of LiCoO₂ (Sherrett-Westaim Company) and 3.60 g of TiO₂(Aldrich Chemical) were used. The precursors were initially pre-mixedusing a mortar and pestle and the mixture was then pelletized. Thepellet was then transferred to a temperature-controlled tube furnaceequipped with an argon gas flow. The sample was heated at a ramp rate of2°/minute to an ultimate temperature of 900° C. and maintained at thistemperature for 8 hours. The sample was then cooled to room temperature,before being removed from the tube furnace for analysis. The powderizedsample showed good uniformity, was very hard and appeared turquoiseblue-green in color.

[0122]FIG. 6 shows the x-ray diffraction pattern for this LiCoTiO₄sample. The data appear fully consistent with the published data ofArillo et al. Solid State Ionics 107, 307 (1998) for the compositionallysimilar LiFeTiO₄. In the Fe material the x-ray diffraction data isconsistent for a cubic spinel structure with the space group Fd3m.

Example 9 Preparation of LiNiTiO₄ from Li₂CO₃/TiO₂/2NiCO₃.3Ni(OH)₂.4H₂O

[0123] The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.2[2NiCO₃.3Ni(OH)₂.4H₂O]→LiNiTiO₄+0.9CO₂+1.4H₂O

[0124] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

[0125] 1.0 g-mol of TiO₂ is equivalent to 79.88 g

[0126] 0.2 g-mol of 2NiCO₃.3Ni(OH)₂.4H₂O is equivalent to 117.5 g

[0127] 2.08 g of Li₂CO₃ (Pacific Lithium Company), 4.49 g of TiO₂(Aldrich Chemical) and 6.63 g of 2NiCO₃.3Ni(OH)₂.4H₂O (Aldrich Chemical)were used. The precursors were initially pre-mixed using a mortar andpestle and the mixture was then pelletized. The pellet was thentransferred to a temperature-controlled tube furnace equipped with anoxygen gas flow. The sample was heated at a ramp rate of 2°/minute to anultimate temperature of 850° C. and maintained at this temperature for 8hours. The sample was then cooled to room temperature, before beingremoved from the tube furnace for analysis. The powderized sample showedreasonable uniformity, was soft and appeared mainly yellow in color.

Example 10 Preparation of LiMZrO₄ from Li₂CO₃/ZrO₂/M₂O₃

[0128] The general reaction may be summarized:

0.5Li₂CO₃+ZrO₂+0.5M₂O₃→LiMZrO₄+0.5CO₂.

[0129] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g.

[0130] 1.0 g-mol of ZrO₂ is equivalent to 123.22 g.

[0131] 0.5 g-mol of M₂O₃ varies according to M.

[0132] The reaction is carried out according to the conditions ofExample 1. Preferably, the temperature of reaction is above 1000° toreact the ZrO₂.

Example 11 Preparation of LiMZr_(1−x)Ti_(x)O₄ from Li₂CO₃/TiO₂/ZrO₂/M₂O₃

[0133] The general scheme is

[0134] The reaction for x=0.5 may be summarized:

0.5Li₂CO₃+0.5ZrO₂+0.5TiO₂+0.5M₂O₃→LiMZr_(0.5)Ti_(0.5)O₄

[0135] 0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g.

[0136] 0.5 g-mol of ZrO₂ is equivalent to 61.61 g.

[0137] 0.5 g-mol of TiO₂ is equivalent to 39.94 g.

[0138] 0.5 g-mol of M₂O₃ varies according to M.

[0139] The reaction is carried out according to the conditions ofExample 1. Preferably, the temperature of reaction is above 1000° toreact the ZrO₂.

Example 12 Preparation of LiMZr_(1−x)Ti_(x)O_(x)—Using Hydrogen

[0140] The general reaction for x=0.5 and for M=vanadium may besummarized.

0.5Li₂CO₃+0.5ZrO₂+0.5TiO₂+0.5V₂O₅+H₂→LiMZr_(0.5)Ti_(0.5)O₄+0.5CO₂+H₂O

[0141] 0.5 g-mol of Li₂CO₃=36.95 g

[0142] 0.5 g-mol of ZrO₂=61.61 g

[0143] 0.5 g-mol of TiO₂=39.94 g

[0144] 0.5 g-mol of V₂O₅=90.94 g

[0145] The reaction is carried out according to Example 3. Preferably,the temperature of reaction is above 1000° to react the ZrO₂.

Example 13 Preparation of LiMZr_(1−x)Ti_(x)O₄ by Carbothermal Reduction

[0146] The general reaction for the case where M is vanadium may besummarized:

0.5Li₂CO₃+(1−x)ZrO₂+xTiO₂+0.5V₂O₅+C→LiVZr_(1−x)Ti_(x)O₄+0.5CO₂+CO

[0147] For x=0.5:

[0148] 0.5 g-mol of Li₂CO₃=36.95 g

[0149] 0.5 g-mol of ZrO₂=61.61 g

[0150] 0.5 g-mol of TiO₂=39.94 g

[0151] 0.5 g-mol of V₂O₅=90.94 g

[0152] 1.0 g-mol of carbon=12.00 g

[0153] The reaction is carried out according to Example 4. Assumes C→COreaction scheme for carbothermal reduction. Excess carbon, for exampleup to 100% weight excess, may be used. Preferably, the temperature ofreaction is in the range of 700-1050° C.

Example 14 Preparation of LiM′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

[0154] Examples of non-transition metals: B, Al, Ga and In, all of whichare normally available as M″₂O₃ oxides e.g. Al(OH)₃, Ga(OH₃), In(OH)₃.They are also available as M″(OH)₃ hydroxides, e.g., Al(OH)₃, Ga(OH)₃and In(OH)₃.

[0155] The general reaction scheme is:

[0156] The reaction requires:

[0157] 0.5 g-mol of Li₂CO₃

[0158] (1−b) g-mol of ZrO₂

[0159] (b) g-mol of TiO₂

[0160] a/2 g-mol of M′₂O₃

[0161] (1−a)/2 g-mol of M″₂O₃

[0162] Reaction is carried out as in Example 1. A temperature above1000° C. may be necessary to react ZrO₂.

[0163] Electrochemical Characterization of Active Materials:

[0164] For electrochemical evaluation purposes the active materials werecycled against a lithium metal counter electrode. The active materialswere used to formulate the positive electrode. The electrode wasfabricated by solvent casting a slurry of the active material,conductive carbon, binder and solvent. The conductive carbon used wasSuper P (MMM Carbon). Kynar® Flex 2801 was used as the binder andelectronic grade acetone was used as the solvent. The slurry was castonto glass and a free-standing electrode film was formed as the solventevaporated. The proportions are as follows on a weight basis: 80% activematerial; 8% Super P carbon; and 12% Kynar binder.

[0165] For all electrochemical measurements the liquid electrolyte wasethylene carbonate/dimethyl carbonate, EC/DMC (2:1 by weight) and 1 MLiPF6. This was used in conjunction with a Glass Fiber filter to formthe anode-cathode separator. Routine electrochemical testing was carriedout on a commercial battery cycler using constant current cyclingbetween pre-set voltage limits. High-resolution electrochemical datawere collected using the Electrochemical Voltage Spectroscopy (EVS)technique. Such technique is known in the art as described in Synth.Met. D217 (1989); Synth. Met. 32, 43 (1989); J. Power Sources, 52,185(1994); and Electrochimica Acta 40, 1603 (1995).

[0166] Electrochemical Characterization of LiVTiO₄

[0167]FIG. 7 (Cell#908086) shows the first cycle constant current dataof the LiVTiO₄ material made from Li₂CO₃/TiO₂/V₂O₃. The data werecollected using a lithium metal counter electrode at 0.2 mA/cm² between2.00 and 4.00 V and are based upon 27.2 mg of the LiVTiO₄ activematerial in the positive electrode. The testing was carried out at 23°C. The initial measured open circuit voltage (OCV) was approximately2.70 V vs. Li. Lithium is extracted from the LiVTiO₄ during charging ofthe cell. A charge equivalent to a material specific capacity of 84mAh/g is extracted from the cell. The theoretical specific capacity forLiVTiO₄ (assuming all the lithium is extracted) is 158 mAh/g.Consequently, the positive electrode active material corresponds toLi_(1−x)VTiO₄ where x equates to about 0.53, when the active material ischarged to about 4.00 V vs. Li. When the cell is discharged toapproximately 2.00 V a quantity of lithium is re-inserted into theLi_(1−x)VTiO₄. The re-insertion process corresponds to approximately 87mAh/g, indicating a good reversibility of the LiVTiO₄ material. At 2.00V the positive active material corresponds to approximatelyLi_(1.02)VTiO₄. The generally symmetrical nature of the charge-dischargecurves further indicates the good reversibility of the system.

[0168] The LiVTiO₄ material made from Li₂CO₃/TiO₂/V₂O₃ was furthersubjected to high resolution electrochemical testing using theElectrochemical Voltage Spectroscopy (EVS) technique. FIG. 8 shows theelectrode voltage versus specific capacity data for this material whencycled between voltage limits of 2.40 and 3.40 V. The weight of theactive material was 35.3 mg and the test was carried out at 23° C. Acharge equivalent to a material specific capacity of 82 mAh/g isextracted from the cell. Thus, when fully charged the positive electrodeactive material, represented by Li_(1−x)VTiO₄, corresponds toLi_(0.48)VTiO₄. The re-insertion process corresponds to approximately 78mAh/g, indicating a good reversibility of the LiVTiO₄ material. Thecapacity corresponding to the lithium extraction process is essentiallythe same as the capacity corresponding to the subsequent lithiuminsertion process. Thus, there is essentially no capacity loss. FIG. 9,the differential capacity data, also indicates good reversibility. Thesymmetrical nature of the peaks indicates the good electrochemicalreversibility. Further, there is low peak separation (charge/discharge)and good correspondence between the broad peak above and below the zeroaxis. There are essentially no peaks that can be related to irreversiblereactions. Overall, this EVS test demonstrates that the preparativeprocedure used to make this material produces a high quality electrodematerial.

[0169]FIG. 10 (Cell#908087) shows the first cycle constant current dataof the LiVTiO₄ material made from LiOH.H₂O/TiO₂/V₂O₃. The data werecollected using a lithium metal counter electrode at 0.2 mA/cm² between2.00 and 4.00 V and are based upon 22.6 mg of the LiVTiO₄ activematerial in the positive electrode. The testing was carried out at 23°C. The initial measured open circuit voltage (OCV) was approximately2.80 V vs. Li. Lithium is extracted from the LiVTiO₄ during charging ofthe cell. A charge equivalent to a material specific capacity of 80mAh/g is extracted from the cell. The theoretical specific capacity forLiVTiO₄ (assuming all the lithium is extracted) is 158 mAh/g.Consequently, the positive electrode active material corresponds toLi_(1−x)VTiO₄ where x equates to about 0.51, when the active material ischarged to about 4.00 V vs. Li. When the cell is discharged toapproximately 2.00 V a quantity of lithium is re-inserted into theLi_(1−x)VTiO₄. The re-insertion process corresponds to approximately 79mAh/g, indicating excellent reversibility of the LiVTiO₄ material. At2.00 V the positive active material corresponds to approximatelyLi_(1.00)VTiO₄. The generally symmetrical nature of the charge-dischargecurves further indicates the good reversibility of the system. The datacollected from this material is fully consistent with the equivalentdata collected—shown above—for the LiVTiO₄ made from Li₂CO₃/TiO₂/V₂O₃route.

[0170] It has been noted above that about 50% of the available lithiumis extracted from the LiVTiO₄ structure. Without being bound by theory,it is likely that the structure of all LiMTiO₄ materials may becharacterized as cubic spinel with the space group Fd3m. The cubicspinel structure, A[B₂]O4 is characterized by cubic-closed packed oxygenions occupying the 32e sites, the A cations located in the tetrahedral8a sites and the B cations located in octahedral 16d sites. This is thesame structure as the lithiated manganese spinel LiMn₂O₄, the well-knowncathode active material used in commercial lithium ion applications. Instoichiometric LiMn₂O₄ spinel, in which the alkali metal cations are alllocated in the tetrahedral 8a sites and the Mn cations occupy theoctahedral 16c sites, it is possible to extract almost all the lithiumfrom the structure. In the paper by Arillo et al. it is reported that inthe LiFeTiO₄ structure there exists a different situation in which thereis a distribution of alkali metal cations over both the 8a and 16 csites. Thus, only about 50% of the lithium cations are actually locatedon the tetrahedral 8a sites, the remaining lithium cations located inthe octahedral sites. This suggests that only around half the lithiumions will be available for extraction and therefore only 50% of thetheoretical specific capacity would be realized in operation. This isclose to what is observed experimentally in this work.

[0171] Electrochemical Characterization of LiCrTiO₄

[0172] The LiCrTiO₄ material made from Li₂CO₃/TiO₂/Cr₂O₃ was testedusing the Electrochemical Voltage Spectroscopy (EVS) technique. FIG. 11shows the electrode voltage versus specific capacity data for thismaterial when cycled between voltage limits of 3.40 and 4.80 V. Theweight of the active material was 11.1 mg and the test was carried outat 23° C. A charge equivalent to a material specific capacity of 37mAh/g is extracted from the cell. The re-insertion process correspondsto approximately 13 mAh/g, indicating a relatively high irreversiblecapacity loss for the EVS cycle. Bearing in mind the extremely highoperating voltage for this material—around 4.6 V vs. Li—the level ofirreversibility is not surprising. At such extreme operating potentialsit is well known that the electrochemical system will become veryunstable. Several irreversible reactions will be expected to occur, suchas electrolyte solvent electrolysis, electrode binder breakdown, as wellas positive electrode current-collector degradation. These factors willdetrimentally affect the experimental results. What is particularlyinteresting is the fact that there still exists significant (reversible)electrode activity at such high potentials. Indeed, it is probable thatin a more stable electrolyte system a significantly higher specificcapacity would be realized. There are very few known insertion materialsthat can operate at such oxidative conditions as those shown here forthe LiCrTiO₄.

[0173]FIG. 12, the differential capacity data, also indicates theLiCrTiO₄ material insertion activity. Close inspection of this figureallows the reversible insertion reactions to be resolved—part of thebroad charge peak above the x-axis is clearly reversible during theinsertion process shown below the x-axis. However, as expected from thehigh irreversible capacity loss described in FIG. 10, there are clearlyother non-reversible reactions also occurring during the cycle.

[0174] In separate experiments the discharge or lithium insertionproperties of the as-made LiCrTiO₄ material were probed. Suchmeasurements are useful in determining the low voltage insertionbehavior of materials in order to evaluate these compounds as potentialnegative (anode) materials for lithium ion cells. In such trials on theLiCrTiO₄ material, three possible reduction reactions may be proposed:

LiCr³⁺Ti⁴⁺O₄+Li⁺+e→Li₂Cr²⁺Ti⁴⁺O₄  (1)

LiCr³⁺Ti⁴⁺O₄+2Li⁺+2e→Li₃Cr³+Ti²⁺O₄  (2)

LiCr³⁺Ti⁴⁺O₄+3Li⁺+3e→Li₄Cr²⁺Ti²⁺O₄  (3)

[0175] Based on a molecular mass of 170.8 for LiCrTiO₄, approximatespecific capacities of 157 mAh/g, 314 mAh/g and 471 mAh/g may becalculated for the reactions (1), (2) and (3) respectively.

[0176] The anode properties of the LiCrTiO₄ material were probed usingthe EVS method. FIG. 13 shows the electrode voltage versus specificcapacity data for the LiCrTiO₄ material when cycled between voltagelimits of 2.00 and 1.00 V. The weight of the active material was 22.2 mgand the test was carried out at 23° C. During the discharge process theactive material may be represented as Li_(1+x)CrTiO₄ indicating theincreasing amount of Li in the structure. The material demonstrates aflat voltage plateau at around 1.5 V vs. Li, indicating the insertion oflithium into the structure. The discharge process is equivalent to aspecific capacity of around 103 mAh/g and based on its molecular mass,the stoicheometry of the active material when discharged to 1.00 V, maybe estimated as Li_(1.66)CrTiO₄. When subsequently charged to 2.00 V, acharge equivalent to a material specific capacity of 94 mAh/g isextracted from the cell indicating the excellent reversibility of theLiCrTiO₄ material. In the fully charged state, the active materialcorresponds to approximately Li_(1.06)CrTiO₄. The generally symmetricalnature of the charge-discharge curve, and the small voltage difference,further indicates the good reversibility of the system.

[0177]FIG. 14, the differential capacity data, indicates excellentreversibility. The symmetrical nature of the peaks indicates goodelectrochemical reversibility; there is very small peak separation(discharge/charge) and good correspondence between peaks above and belowthe zero axis. There are essentially no peaks that can be related toirreversible reactions, since the peak above the axis (cell charge) hasa corresponding peak below the axis (cell discharge). These datademonstrate that the preparative procedure used to make this materialproduces a high quality electrode material.

We claim:
 1. An electrode composition comprising a polymeric binder;electrically conductive material; and an active material selected fromthe group of compounds of general formulaLi_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄ wherein n is from about 0.01 to 2,a is greater than zero and less than or equal to 1, b is greater than orequal to zero and less than or equal to 1, M′ comprises one or moretransition metals selected from the group consisting of titanium,vanadium, manganese, iron, chromium, nickel, cobalt, molybdenum,niobium, and combinations thereof, with the proviso that when b is 1, M′comprises at least vanadium, and M″ is selected from the groupconsisting of aluminum, boron, indium, gallium, antimony, bismuth,thallium, and combinations thereof.
 2. An electrode compositionaccording to claim 1, wherein the electrically conductive materialcomprises carbon.
 3. An electrode composition according to claim 1,wherein n is
 1. 4. An electrode composition according to claim 1,wherein M′ comprises vanadium.
 5. An electrode composition according toclaim 1, wherein b is
 1. 6. An electrode composition according to claim1, wherein b is
 0. 7. A battery comprising an electrochemical cell,wherein the electrochemical cell comprises an anode, a cathode, and anelectrolyte, wherein the cathode comprises an electrode compositionaccording to claim
 1. 8. A rechargeable battery comprising anelectrochemical cell wherein the electrochemical cell comprises acathode, an anode, and an electrolyte, wherein the cathode in a firstcondition comprises an active material selected from the group ofcompounds of general formula Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄wherein n is from about 0.01 to 2, a is greater than zero and less thanor equal to 1, b is greater than or equal to 0 and less than or equal to1, M′ comprises one or more transition metals selected from the groupconsisting of titanium, vanadium, manganese, iron, chromium, nickel,cobalt, molybdenum, and niobium, with the proviso that when b is 1, M′comprises at least vanadium, and M″ is selected from the groupconsisting of aluminum, boron, indium, gallium, antimony, bismuth,thallium, and combinations thereof.
 9. A rechargeable battery accordingto claim 8, wherein M′ comprises at least vanadium.
 10. A rechargeablebattery according to claim 8, wherein n is
 1. 11. A rechargeable batteryaccording to claim 8, wherein b is
 1. 12. A rechargeable batteryaccording to claim 8, wherein b is
 0. 13. A rechargeable batteryaccording to claim 8, wherein the cathode comprises an active materialrepresented by the formula Li_(n−c)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄wherein in the first condition c is zero, and in a second condition c isgreater than zero.
 14. A rechargeable battery according to claim 13,wherein the first condition corresponds to an uncharged state and thesecond condition corresponds to a charged or partially charged state.15. A method of operating a battery, comprising the steps of a)providing an electrochemical cell in a discharged state wherein the cellcomprises a cathode, an anode, and an electrolyte and wherein thecathode comprises an active material selected from the group ofcompounds of general formula Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄ wherein n is from about 0.01 to 2, a is greater than zero and less thanor equal to 1, b is greater than or equal to zero and less than or equalto 1, M′ comprises one or more transition metals selected from the groupconsisting of titanium, vanadium, manganese, iron, chromium, nickel,cobalt, molybdenum, niobium, and combinations thereof, with the provisothat when b is 1, M′ comprises at least vanadium, and M″ is selectedfrom the group consisting of aluminum, boron, indium, gallium, antimony,bismuth, thallium, and combinations thereof; b) charging the cell; andc) discharging the cell.
 16. A method according to claim 15, wherein bis 1 and M′ comprises at least vanadium.
 17. A method according to claim15, wherein the active material comprises LiVTiO₄.
 18. A methodaccording to claim 15, wherein b is not
 1. 19. A method according toclaim 15, wherein M′ comprises at least vanadium.
 20. A rechargeablebattery comprising an electrochemical cell wherein the electrochemicalcell comprises a cathode, an anode, and an electrolyte, wherein thecathode in a first condition comprises an active material selected fromthe group of compounds of general formula Li_(n)VTiO₄ wherein n is from0.01 to about
 2. 21. A rechargeable battery according to claim 20,wherein n is greater than 0.2.
 22. A rechargeable battery according toclaim 20, wherein n is
 1. 23. A rechargeable battery according to claim20, wherein the cathode comprises an active material represented by theformula Li_(n−c)VTiO₄ wherein in the first condition c is zero and in asecond condition c is greater than zero.
 24. A rechargeable batteryaccording to claim 23, wherein the first condition corresponds to anuncharged state and the second condition corresponds to a charged orpartially charged state.
 25. A rechargeable battery according to claim20, wherein the anode comprises an insertion material.
 26. Arechargeable battery according to claim 20, wherein the anode comprisesa carbonaceous insertion material.
 27. A rechargeable battery comprisingan electrochemical cell wherein the electrochemical cell comprises acathode, an anode, and an electrolyte, wherein the cathode in a firstcondition comprises an active material selected from the group ofcompounds of general formula Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄wherein a is greater than zero and less than or equal to 1; b is lessthan one and greater than or equal to zero; n is from 0.02 to about 2;M′ comprises one or more transition metals selected from the groupconsisting of titanium, vanadium, manganese, iron, chromium, nickel,cobalt, molybdenum, and niobium, and M″ is selected from the groupconsisting of aluminum, boron, indium, gallium, antimony, bismuth,thallium, and combinations thereof.
 28. A rechargeable battery accordingto claim 27, wherein the anode comprises an insertion material.
 29. Arechargeable battery according to claim 27, wherein the anode comprisesa carbonaceous insertion material.
 30. A rechargeable battery accordingto claim 27, wherein n is
 1. 31. A rechargeable battery according toclaim 27, wherein the cathode comprises an active material representedby the formula Li_(n−c)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄ wherein in thefirst condition c is 0, and in a second condition, c is greater than 0.32. A rechargeable battery according to claim 31, wherein the firstcondition corresponds to a discharged state and the second conditioncorresponds to a charged or partially charged state.
 33. A rechargeablebattery comprising an electrochemical cell wherein the electrochemicalcell comprises a cathode, an anode, and an electrolyte, wherein theanode in a first condition comprises at least one active materialselected from the group of compounds of general formulaLi_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄ wherein n is from about 0.01 to 2,a is greater than zero and less than or equal to 1, b is greater than orequal to 0 and less than or equal to 1, M′ comprises one or moretransition metals selected from the group consisting of titanium,vanadium, manganese, iron, chromium, nickel, cobalt, molybdenum,niobium, and combinations thereof, and M″ is selected from the groupconsisting of aluminum, boron, indium, gallium, antimony, bismuth,thallium, and combinations thereof.
 34. A rechargeable battery accordingto claim 33, wherein M′ comprises at least chromium.
 35. A rechargeablebattery according to claim 33, wherein n is
 1. 36. A rechargeablebattery according to claim 33, wherein the active material isrepresented by the formula LiCrTiO₄.
 37. A rechargeable batteryaccording to claim 33, wherein the anode comprises an active materialrepresented by the formula Li_(n+c)MTiO₄ wherein in the first conditionc is 0, and in a second condition, c is greater than
 0. 38. Arechargeable battery according to claim 37, wherein the first conditioncorresponds to a uncharged state and the second condition corresponds toa charged or partially charged state.